arXiv subjects

Ralf Bender

Publications and source records attributed to Ralf Bender.

At least 91 records · Page 5Linked to original sources

arXiv2011

The HETDEX Pilot Survey. II. The Evolution of the Ly-alpha Escape Fraction from the UV Slope and Luminosity Function of 1.9<z<3.8 LAEs

We study the escape of Ly-alpha photons from Ly-alpha emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9<z<3.8 detected through integral-field spectroscopy of blank fields by the HETDEX Pilot Survey. For 89 LAEs showing counterparts in deep broad-band images we measure the rest-frame UV luminosity and the UV slope, which we use to estimate E(B-V) under the assumption of a constant intrinsic UV slope for LAEs. These two quantities are used to measure the dust-corrected star formation rate (SFR). A comparison between the observed Ly-alpha luminosity and that predicted by the dust-corrected SFR yields the Ly-alpha escape fraction. We also measure the Ly-alpha luminosity function. Integration of the luminosity function provides a measurement of the Ly-alpha luminosity density across our redshift range. We combine our data with that from other surveys at 0.3<z<7.7 to trace the evolution of the Ly-alpha luminosity density. We then compare it to that expected from the star-formation history of the universe in order to characterize the evolution of the Ly-alpha escape fraction of the overall galaxy population [abriged]

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arXiv2011

Supermassive black holes do not correlate with dark matter halos of galaxies

Supermassive black holes have been detected in all galaxies that contain bulge components when the galaxies observed were close enough so that the searches were feasible. Together with the observation that bigger black holes live in bigger bulges, this has led to the belief that black hole growth and bulge formation regulate each other. That is, black holes and bulges "coevolve". Therefore, reports of a similar correlation between black holes and the dark matter halos in which visible galaxies are embedded have profound implications. Dark matter is likely to be nonbaryonic, so these reports suggest that unknown, exotic physics controls black hole growth. Here we show - based in part on recent measurements of bulgeless galaxies - that there is almost no correlation between dark matter and parameters that measure black holes unless the galaxy also contains a bulge. We conclude that black holes do not correlate directly with dark matter. They do not correlate with galaxy disks, either. Therefore black holes coevolve only with bulges. This simplifies the puzzle of their coevolution by focusing attention on purely baryonic processes in the galaxy mergers that make bulges.

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arXiv2010

HETDEX pilot survey for emission-line galaxies - I. Survey design, performance, and catalog

We present a catalog of emission-line galaxies selected solely by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivated as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information for 397 emission-line galaxies detected over 169 sq.arcmin with a 3500-5800 Ang. bandpass under 5 Ang. full-width-half-maximum (FWHM) spectral resolution. The survey's best sensitivity for unresolved objects under photometric conditions is between 4-20 E-17 erg/s/sq.cm depending on the wavelength, and Ly-alpha luminosities between 3-6 E42 erg/s are detectable. This survey method complements narrowband and color-selection techniques in the search for high redshift galaxies with its different selection properties and large volume probed. The four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complementary data. We find 104 galaxies via their high redshift Ly-alpha emission at 1.9 44 sq.arcsec which appear to be extended Ly-alpha nebulae. We also find three high-z objects with rest frame Ly-alpha equivalent widths above the level believed to be achievable with normal star formation, EW(rest)>240 Ang.

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arXiv2010

Bulgeless Giant Galaxies Challenge our Picture of Galaxy Formation by Hierarchical Clustering

We dissect giant Sc-Scd galaxies with Hubble Space Telescope photometry and Hobby-Eberly Telescope spectroscopy. We use HET's High Resolution Spectrograph (resolution = 15,000) to measure stellar velocity dispersions in the nuclear star clusters and pseudobulges of the pure-disk galaxies M33, M101, NGC 3338, NGC 3810, NGC 6503, and NGC 6946. We conclude: (1) Upper limits on the masses of any supermassive black holes are MBH <= (2.6+-0.5) * 10**6 M_Sun in M101 and MBH <= (2.0+-0.6) * 10**6 M_Sun in NGC 6503. (2) HST photometry shows that the above galaxies contain tiny pseudobulges that make up <~ 3 % of the stellar mass but no classical bulges. We inventory a sphere of radius 8 Mpc centered on our Galaxy to see whether giant, pure-disk galaxies are common or rare. In this volume, 11 of 19 galaxies with rotation velocity > 150 km/s show no evidence for a classical bulge. Four may contain small classical bulges that contribute 5-12% of the galaxy light. Only 4 of the 19 giant galaxies are ellipticals or have classical bulges that contribute 1/3 of the galaxy light. So pure-disk galaxies are far from rare. It is hard to understand how they could form as the quiescent tail of a distribution of merger histories. Recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation more acute: How can hierarchical clustering make so many giant, pure-disk galaxies with no evidence for merger-built bulges? This problem depends strongly on environment: the Virgo cluster is not a puzzle, because >2/3 of its stellar mass is in merger remnants.

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arXiv2010

The central black hole mass of the high-sigma but low-bulge-luminosity lenticular galaxy NGC 1332

The masses of the most massive supermassive black holes (SMBHs) predicted by the M_BH-sigma and M_BH-luminosity relations appear to be in conflict. Which of the two relations is the more fundamental one remains an open question. NGC 1332 is an excellent example that represents the regime of conflict. It is a massive lenticular galaxy which has a bulge with a high velocity dispersion sigma of ~320 km/s; bulge--disc decomposition suggests that only 44% of the total light comes from the bulge. The M_BH-sigma and the M_BH-luminosity predictions for the central black hole mass of NGC 1332 differ by almost an order of magnitude. We present a stellar dynamical measurement of the SMBH mass using an axisymmetric orbit superposition method. Our SINFONI integral-field unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence which has a diameter of ~0.76 arcsec. The sigma inside 0.2 arcsec reaches ~400 km/s. The IFU data allow us to increase the statistical significance of our results by modelling each of the four quadrants separately. We measure a SMBH mass of (1.45 \pm 0.20) x 10^9 M_sun with a bulge mass-to-light ratio of 7.08 \pm 0.39 in the R-band. With this mass, the SMBH of NGC 1332 is offset from the M_BH-luminosity relation by a full order of magnitude but is consistent with the M_BH-sigma relation.

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arXiv2010

Measurements of the Rate of Type Ia Supernovae at Redshift z < ~0.3 from the SDSS-II Supernova Survey

We present a measurement of the volumetric Type Ia supernova (SN Ia) rate based on data from the Sloan Digital Sky Survey II (SDSS-II) Supernova Survey. The adopted sample of supernovae (SNe) includes 516 SNe Ia at redshift z \lesssim 0.3, of which 270 (52%) are spectroscopically identified as SNe Ia. The remaining 246 SNe Ia were identified through their light curves; 113 of these objects have spectroscopic redshifts from spectra of their host galaxy, and 133 have photometric redshifts estimated from the SN light curves. Based on consideration of 87 spectroscopically confirmed non-Ia SNe discovered by the SDSS-II SN Survey, we estimate that 2.04+1.61-0.95 % of the photometric SNe Ia may be misidentified. The sample of SNe Ia used in this measurement represents an order of magnitude increase in the statistics for SN Ia rate measurements in the redshift range covered by the SDSS-II Supernova Survey. If we assume a SN Ia rate that is constant at low redshift (z < 0.15), then the SN observations can be used to infer a value of the SN rate of rV = (2.69+0.34+0.21-0.30-0.01) x10^{-5} SNe yr^{-1} Mpc-3 (H0 /(70 km s^{-1} Mpc^{-1}))^{3} at a mean redshift of ~ 0.12, based on 79 SNe Ia of which 72 are spectroscopically confirmed. However, the large sample of SNe Ia included in this study allows us to place constraints on the redshift dependence of the SN Ia rate based on the SDSS-II Supernova Survey data alone. Fitting a power-law model of the SN rate evolution, r_V(z) = A_p x ((1 + z)/(1 + z0))^ν, over the redshift range 0.0 < z < 0.3 with z0 = 0.21, results in A_p = (3.43+0.15-0.15) x 10^{-5} SNe yr^{-1} Mpc-3 (H0 /(70 km s^{-1} Mpc^{-1}))^{3} and ν= 2.04+0.90-0.89.

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arXiv2010

A Measurement of the Rate of Type Ia Supernovae in Galaxy Clusters from the SDSS-II Supernova Survey

ABRIDGED We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z <0.17 and 27 SN events in 492 maxBCG clusters at 0.1 < z < 0.3$. We find values for the cluster SN Ia rate of $({0.37}^{+0.17+0.01}_{-0.12-0.01}) \mathrm{SNu}r h^{2}$ and $({0.55}^{+0.13+0.02}_{-0.11-0.01}) \mathrm{SNu}r h^{2}$ ($\mathrm{SNu}x = 10^{-12} L_{x\sun}^{-1} \mathrm{yr}^{-1}$) in C4 and maxBCG clusters, respectively, where the quoted errors are statistical and systematic, respectively. The SN rate for early-type galaxies is found to be $({0.31}^{+0.18+0.01}_{-0.12-0.01}) \mathrm{SNu}r h^{2}$ and $({0.49}^{+0.15+0.02}_{-0.11-0.01})$ $\mathrm{SNu}r h^{2}$ in C4 and maxBCG clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is found to be $({2.04}^{+1.99+0.07}_{-1.11-0.04}) \mathrm{SNu}r h^{2}$ and $({0.36}^{+0.84+0.01}_{-0.30-0.01}) \mathrm{SNu}r h^{2}$ in C4 and maxBCG clusters. The ratio of the SN Ia rate in cluster early-type galaxies to that of the SN Ia rate in field early-type galaxies is ${1.94}^{+1.31+0.043}_{-0.91-0.015}$ and ${3.02}^{+1.31+0.062}_{-1.03-0.048}$, for C4 and maxBCG clusters. The SN rate in galaxy clusters as a function of redshift...shows only weak dependence on redshift. Combining our current measurements with previous measurements, we fit the cluster SN Ia rate data to a linear function of redshift, and find $r_{L} = $ $[(0.49^{+0.15}_{-0.14}) +$ $(0.91^{+0.85}_{-0.81}) \times z]$ $\mathrm{SNu}B$ $h^{2}$. A comparison of the radial distribution of SNe in cluster to field early-type galaxies shows possible evidence for an enhancement of the SN rate in the cores of cluster early-type galaxies... we estimate the fraction of cluster SNe that are hostless to be $(9.4^+8._3-5.1)%$.

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arXiv2010

The Deep SWIRE Field. IV. First properties of the sub-mJy galaxy population: redshift distribution, AGN activity and star formation

We present a study of a 20cm selected sample in the Deep SWIRE VLA Field, reaching a limiting flux density of ~13.5 uJy at the image center. In a 0.6x0.6 square degrees field, we are able to assign an optical/IR counterpart to 97% of the radio sources. Up to 11 passbands from the NUV to 4.5um are then used to sample the spectral energy distribution (SED) of these counterparts in order to investigate the nature of the host galaxies. By means of an SED template library and stellar population synthesis models we estimate photometric redshifts, stellar masses, and stellar population properties, dividing the sample in three sub-classes of quiescent, intermediate and star-forming galaxies. We focus on the radio sample in the redshift range 0.3<z<1.3 where we estimate to have a redshift completeness higher than 90%, and study the properties and redshift evolution of these sub-populations. We find that, as expected, the relative contributions of AGN and star-forming galaxies to the uJy population depend on the flux density limit of the sample. At all flux levels a significant population of "green-valley" galaxies is observed. While the actual nature of these sources is not definitely understood, the results of this work may suggest that a significant fraction of faint radio sources might be composite (and possibly transition) objects, thus a simple "AGN vs star-forming" classification might not be appropriate to fully understand what faint radio populations really are.

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arXiv2009

Do black hole masses scale with classical bulge luminosities only? The case of the two composite pseudobulge galaxies NGC3368 and NGC3489

It is now well established that all galaxies with a massive bulge component harbour a central supermassive black hole (SMBH). The mass of the SMBH correlates with bulge properties such as the bulge mass and the velocity dispersion, which implies that the bulge and the SMBH of a galaxy have grown together during the formation process. The spiral galaxy NGC3368 and the S0 galaxy NGC3489 both host a pseudobulge and a much smaller classical bulge component at the centre. We present high resolution, near-infrared IFU data of these two galaxies, taken with SINFONI at the VLT, and use axisymmetric orbit models to determine the masses of the SMBHs. The SMBH mass of NGC3368 is M_BH=7.5x10^6 M_sun with an error of 1.5x10^6 M_sun, which mostly comes from the non-axisymmetry in the data. For NGC3489, a solution without black hole cannot be excluded when modelling the SINFONI data alone, but can be clearly ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for which we obtain M_BH=6.00^{+0.56}_{-0.54} (stat) +/- 0.64 (sys) x 10^6 M_sun. Although both galaxies seem to be consistent with the M_BH-sigma relation, at face value they do not agree with the relation between bulge magnitude and black hole mass when the total bulge magnitude (i.e., including both classical bulge and pseudobulge) is considered; the agreement is better when only the small classical bulge components are considered. However, taking into account the ageing of the stellar population could change this conclusion.

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arXiv2009

First-year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results: Hubble Diagram and Cosmological Parameters

We present measurements of the Hubble diagram for 103 Type Ia supernovae (SNe) with redshifts 0.04 < z < 0.42, discovered during the first season (Fall 2005) of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. These data fill in the redshift "desert" between low- and high-redshift SN Ia surveys. We combine the SDSS-II measurements with new distance estimates for published SN data from the ESSENCE survey, the Supernova Legacy Survey, the Hubble Space Telescope, and a compilation of nearby SN Ia measurements. Combining the SN Hubble diagram with measurements of Baryon Acoustic Oscillations from the SDSS Luminous Red Galaxy sample and with CMB temperature anisotropy measurements from WMAP, we estimate the cosmological parameters w and Omega_M, assuming a spatially flat cosmological model (FwCDM) with constant dark energy equation of state parameter, w. For the FwCDM model and the combined sample of 288 SNe Ia, we find w = -0.76 +- 0.07(stat) +- 0.11(syst), Omega_M = 0.306 +- 0.019(stat) +- 0.023(syst) using MLCS2k2 and w = -0.96 +- 0.06(stat) +- 0.12(syst), Omega_M = 0.265 +- 0.016(stat) +- 0.025(syst) using the SALT-II fitter. We trace the discrepancy between these results to a difference in the rest-frame UV model combined with a different luminosity correction from color variations; these differences mostly affect the distance estimates for the SNLS and HST supernovae. We present detailed discussions of systematic errors for both light-curve methods and find that they both show data-model discrepancies in rest-frame $U$-band. For the SALT-II approach, we also see strong evidence for redshift-dependence of the color-luminosity parameter (beta). Restricting the analysis to the 136 SNe Ia in the Nearby+SDSS-II samples, we find much better agreement between the two analysis methods but with larger uncertainties.

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arXiv2009

The evolution of early and late type galaxies in the COSMOS up to z~1.2

The Cosmic Evolution Survey (COSMOS) allows for the first time a highly significant census of environments and structures up to redshift one, as well as a full morphological description of the galaxy population. In this paper we present a study aimed to constrain the evolution, in the redshift range 0.2 < z < 1.2, of the mass content of different morphological types and its dependence on the environmental density. We use a deep multicolor catalog, covering an area of ~0.7 square degrees inside the COSMOS field, with accurate photometric redshifts (i < 26.5 and dz/(z+1) ~ 0.035). We estimate galaxy stellar masses by fitting the multi-color photometry to a grid of composite stellar population models. We quantitatively describe the galaxy morphology by fitting PSF convolved Sersic profiles to the galaxy surface brightness distributions down to F814 = 24 mag for a sample of 41300 objects. We confirm an evolution of the morphological mix with redshift: the higher the redshift the more disk-dominated galaxies become important. We find that the morphological mix is a function of the local comoving density: the morphology density relation extends up to the highest redshift explored. The stellar mass function of disk-dominated galaxies is consistent with being constant with redshift. Conversely, the stellar mass function of bulge-dominated systems shows a decline in normalization with redshift. Such different behaviors of late-types and early-types stellar mass functions naturally set the redshift evolution of the transition mass. ABRIDGED

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arXiv2009

A Quintet of Black Hole Mass Determinations

We report five new measurements of central black hole masses based on STIS and WFPC2 observations with the Hubble Space Telescope and on axisymmetric, three-integral, Schwarzschild orbit-library kinematic models. We selected a sample of galaxies within a narrow range in velocity dispersion that cover a range of galaxy parameters (including Hubble type and core/power-law surface density profile) where we expected to be able to resolve the galaxy's sphere of influence based on the predicted value of the black hole mass from the M-sigma relation. We find masses in units of 10^8 solar masses for the following galaxies: NGC 3585, M_BH = 3.4 (+1.5, -0.6); NGC 3607, M_BH = 1.2 (+0.4, -0.4); NGC 4026, M_BH = 2.1 (+0.7, -0.4); and NGC 5576, M_BH = 1.8 (+0.3, -0.4), all significantly excluding M_BH = 0. For NGC 3945, M_BH = 0.09 (+0.17, -0.21), which is significantly below predictions from M-sigma and M-L relations and consistent with M_BH = 0, though the presence of a double bar in this galaxy may present problems for our axisymmetric code.

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arXiv2009

The M-sigma and M-L Relations in Galactic Bulges and Determinations of their Intrinsic Scatter

We derive improved versions of the relations between supermassive black hole mass (M_BH) and host-galaxy bulge velocity dispersion (sigma) and luminosity (L) (the M-sigma and M-L relations), based on 49 M_BH measurements and 19 upper limits. Particular attention is paid to recovery of the intrinsic scatter (epsilon_0) in both relations. We find log(M_BH / M_sun) = alpha + beta * log(sigma / 200 km/s) with (alpha, beta, epsilon_0) = (8.12 +/- 0.08, 4.24 +/- 0.41, 0.44 +/- 0.06) for all galaxies and (alpha, beta, epsilon_0) = (8.23 +/- 0.08, 3.96 +/- 0.42, 0.31 +/- 0.06) for ellipticals. The results for ellipticals are consistent with previous studies, but the intrinsic scatter recovered for spirals is significantly larger. The scatter inferred reinforces the need for its consideration when calculating local black hole mass function based on the M-sigma relation, and further implies that there may be substantial selection bias in studies of the evolution of the M-sigma relation. We estimate the M-L relationship as log(M_BH / M_sun) = alpha + beta * log(L_V / 10^11 L_sun,V) of (alpha, beta, epsilon_0) = (8.95 +/- 0.11, 1.11 +/- 0.18, 0.38 +/- 0.09); using only early-type galaxies. These results appear to be insensitive to a wide range of assumptions about the measurement errors and the distribution of intrinsic scatter. We show that culling the sample according to the resolution of the black hole's sphere of influence biases the relations to larger mean masses, larger slopes, and incorrect intrinsic residuals.

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arXiv2009

Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores

High-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L_def and mass deficits M_def associated with the cores of elliptical galaxies. We show that L_def correlates with the velocity dispersion sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L_def correlates with BH mass MBH. Also, the fractional light deficit L_def/L correlates with MBH/M, the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well known correlation between MBH and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with MBH and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. After dry mergers, cores are believed to be scoured by BH binaries that fling stars away as their orbits decay or by BHs that sink back to the center after recoiling from anisotropic gravitational radiation emitted when they merge. Direct evidence has been elusive. We interpret the new correlations as the "smoking gun" that connects cores with BHs. Together, the MBH - sigma and MBH - L_def correlations give us two independent ways to estimate BH masses in core ellipticals.

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arXiv2008

Photometric redshifts for the CFHTLS-Wide

We want to derive bias free, accurate photometric redshifts for those fields of the CFHTLS-Wide data which are covered in the u*, g', r', i' and z' filters and are public on January 2008. These are 37 square degrees in the W1, W3 and W4 fields with photometric data for a total of 2.597.239 galaxies. We use the photometric redshift code PHOTO-z of Bender et al. (2001). We compare our redshifts for the W1, W3 and W4 fields to about 7500 spectroscopic redshifts from the VVDS therein. For galaxies with 17.5 <= i' AB <= 22.5 the accuracies and outlier rates become sigma=0.033, eta~2 % for W1, sigma=0.037, eta~2% for W3 and sigma=0.035, eta~2.5 % outliers for W4 fields. For the total galaxy sample with about 9000 spectroscopic redshifts from VVDS, DEEP2 or SDSS we obtain a sigma=0.04 and eta~5.7% for the PHOTO-z redshifts. We consider the photometric redshifts of Erben et al. (2008) which were obtained with exactly the same photometric catalog using the BPZ-redshift code and compare them with our computed redshifts. We also merge the subsample with good photometric redshifts from PHOTO-z with that one from BPZ to obtain a sample which then contains 'secure' redshifts according to both the PHOTO-z and the BPZ codes. This sample contains about 6100 spectra and the photometric redshift qualities become sigma=0.037 and eta~1.0% for our PHOTO-z redshifts. We conclude that this work provides a bias free, low dispersion photometric redshift catalog, that we have criteria at hand to select a 'robust' subsample with fewer outliers. Such a subsample is very useful to study the redshift dependent growth of the dark matter fluctuations with weak lensing cosmic shear analyses or to investigate the redshift dependent weak lensing signal behind clusters of galaxies in the framework of dark energy equation of state constraints.

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arXiv2008

Structure and Formation of Elliptical and Spheroidal Galaxies

New surface photometry of all known elliptical galaxies in the Virgo cluster is added to published data to derive composite profiles over large dynamic ranges. Sersic functions fit them remarkably well. Effective brightnesses and radii are derived via Sersic fits and by integrating the profiles nonparametrically. We strongly confirm two dichotomies: (1) Elliptical galaxies from cDs to M32 form a tight sequence in Fundamental Plane parameter space that is almost perpendicular to the sequence of spheroidal galaxies from NGC 205 to Draco. This is consistent with our understanding of their different formation processes: mergers for Es and conversion of late-type galaxies into spheroidals by environmental effects and by energy feedback from supernovae. (2) Ellipticals come in two varieties: e.g., our 10 brightest Es have cuspy cores; our 17 fainter Es do not have cores. We find a new distinct component in coreless Es. All have extra light at the center above the inward extrapolation of the outer Sersic profile. We suggest that extra light is made by starbursts in dissipational (wet) mergers, as in numerical simulations. Three other new aspects also point to an explanation of how the E-E dichotomy formed: extra light Es were made in wet mergers while core Es were made in dry mergers. We confirm that core Es do and extra light Es generally do not contain X-ray gas. This suggests why the E-E dichotomy arose. Only core Es and their progenitors are massive enough to retain hot gas that can make dry mergers dry and protect old star populations from late star formation.

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arXiv2008

A Stellar Dynamical Measurement of the Black Hole Mass in the Maser Galaxy NGC 4258

We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These models are constrained by high spatial resolution imaging and long-slit spectroscopy of the nuclear region obtained with the {\em Hubble Space Telescope}, complemented by ground-based observations extending to larger radii. Our best mass estimate is $\MBH = (3.3 \pm 0.2) \times 10^7 \MSun $ for a distance of 7.28 Mpc (statistical errors only). This is within 15% of $ (3.82\pm 0.01) \times 10^7 \MSun$, the mass determined from the kinematics of water masers (rescaled to the same distance) assuming they are in Keplerian rotation in a warped disk. The construction of accurate dynamical models of NGC 4258 is somewhat compromised by an unresolved active nucleus and color gradients, the latter caused by variations in the stellar population and/or obscuring dust. These problems are not present in the $\sim 30$ other black hole mass determinations from stellar dynamics that have been published by us and other groups; thus, the relatively close agreement between the stellar dynamical mass and the maser mass in NGC 4258 enhances our confidence in the black hole masses determined in other galaxies from stellar dynamics using similar methods and data of comparable quality.

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arXiv2008

First-Year Spectroscopy for the SDSS-II Supernova Survey

This paper presents spectroscopy of supernovae discovered in the first season of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for and measures multi-band light curves of supernovae in the redshift range z = 0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our goal is to better characterize the supernova population, with a particular focus on SNe Ia, improving their utility as cosmological distance indicators and as probes of dark energy. Our supernova spectroscopy program features rapid-response observations using telescopes of a range of apertures, and provides confirmation of the supernova and host-galaxy types as well as precise redshifts. We describe here the target identification and prioritization, data reduction, redshift measurement, and classification of 129 SNe Ia, 16 spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first season. We also describe our efforts to measure and remove the substantial host galaxy contamination existing in the majority of our SN spectra.

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